The invention relates to a semiconductor device, more particularly a transistor, notably a power transistor, having a semiconductor body fixed by soldering on a support and having at its surface metallic connection contact areas, including means for protecting from overloads.
A known problem arises due to the lack of heat dissipation in transistors enclosed by a poorly heat-conducting material, notably by an envelope of plastic material. This phenomenon becomes manifest particularly in the case of power transistors for which the effect of an overload of current, of voltage or of energy generally results in the destruction of the two junctions which then form a shortcircuit.
If the transistor is used in a regulation device (for example, regulation of the speed of a motor, regulation of the voltage of an alternator, antilock brake system), the formation of a shortcircuit causes the regulation control to remain locked in its maximum position, which can become catastrophic.
Experience has shown that the shortcircuit is obtained at the transistor when during any overload a zone of small surface area of the semiconductor crystal, generally of silicon, is brought to a temperature such that formation of a eutectic between the semiconductor material and the metallized layer of the contact surface deposited at the surface occurs. This phenomenon becomes more rapid and frequent as the heat wave flows slowly, which is the case notably in devices enclosed by a plastic material.
Experience has also shown that the temperature which leads to this local formation of a eutectic of the semiconductor crystal and of the metallized layer is about 560.degree. C. in the case of a metallized layer of aluminum and of a contact of silicon.
Semiconductor devices comprising integrated circuits, notably programmable memories, are already known, in which fuses are formed. However, as to these devices, the means used are not suitable to solve the problem caused by this undesired formation of a eutectic. Representative prior art devices are shown in U.S. Pat. No. 3,693,048 and Japanese Kokai No. 57-145.357.
Thus, in the case of programmable memories in the form of integrated circuits, the fusible elements have to be voluntarily and selectively destructed at predetermined and comparatively high values of current or energy, which lead to the use of materials which are very resistive and melt at very high temperatures, which are generally much higher than 1000.degree. C.